RELATIONS OF INSECTS TO OTHER ARTHROPODA 23 



median pieces of the gnathochilarium of Diplopoda. Hypopharynx? 

 Epipharynx? 



Trunk with from fifteen to sixteen dorsal, more or less free subequal 

 scutes, the first the smallest. Pedigerous segments twelve; also twelve 

 pairs of 5-jointed legs, which are of nearly equal length, the first pair 4-, 

 the others 5-jointed, all ending in two claws, as in Synaptera and winged 

 insects. A pair of 1 -jointed anal cerci homologous with those of Thy- 

 sanurq and Orthoptera, into each of which opens a large abdominal 

 silk-gland. Abdominal segments ivith movable styles or " pseudopods " 

 (" Parapodia " of Latzel and of Schmidt), like those of Campodea and 

 Machilis, and situated on the base of the coxal joint in front of the ven- 

 tral sac. Within the body near the base of each abdominal style is an 

 eversible coxal sac or blood-gill (Fig. 15, eg). The single genital opening 

 is on the fourth trunk-segment in both sexes (Fig. 15, indicated by the 

 arroiu). The malpighian tubes (ur. fy are two in number, opening into 

 the digestive canal at the anterior end of the hind intestine; they extend 

 in front to the third or second segment from the head. They are broad 

 and straight at their origin, becoming towards the end very slender and 

 convoluted. 



The three divisions of the digestive track are as in insects, the epithe- 

 lium of the mid-gut being histologically as in Campodea and Japyx; 

 rectal glands are present. A pair of very large salivary glands are 

 situated in the first to the fourth trunk-segments, consisting of a glandu- 

 lar portion with its duct, which unite into a common duct opening on 

 the wider side of the head, probably in the labium. 



But a single pair of stigmata is present, and these are situated in the 



front of the head, beneath the insertion of the antennae and within the 



stipes of the mandibles; the tracheae, are very fine, without spiral threads 



(tcenidia), and mostly contained within the head, two fine branches 



extending on each side into the second trunk-segment. 



After birth the body increases in length by the addition of new seg- 

 ments at the growing 'point. 



In respect to the nervous system, there are no diagnostic charac- 

 ters ; there are, however, not as many as two pairs of ganglia to a 

 segment. The brain is well developed, sending a pair of slender 

 nerves to the small eyes. The ganglia of the segment bearing the 

 first pair of legs is fused with the subcesophageal ganglion. Grassi 

 was unable to detect a true sympathetic system, but he suspects the 

 existence of a very small frontal ganglion. 



The slender dorsal vessel, provided with ostia and valvules, pul- 

 sates along the entire length of the trunk; an aorta passes into the 

 head. 



